Mainly that Google intentionally makes its sites (like YouTube or Google Docs) slower and less useable when they detect you're using Firefox, and/or ad blockers (which you need Firefox to use, so same difference).

It's mostly fixable with add-ons and userscripts (and eventually, one hopes, with an antitrust lawsuit), but it's still a hassle.

I very much dislike Mozilla's direction over the last decade. They're introducing user-hostile features that subtly break normal browsing experience, even when disabled[0]. Not like Google is better, but I'm also trying to get away from Mozilla.

[0] On Firefox Mobile, there's a "feature" which makes the address bar auto-complete domains of companies paying Mozilla. I noticed this with Netflix - I never visit, but when I start writing a URL with n, roughly every 10th time Netflix was suggested. You can disable this feature, but this doesn't actually disable it. The address bar no longer auto-completes with Netflix, instead it just doesn't autocomplete! So 9/10 times I can write n and press Enter, but 1/10 times I press n and search for the letter n.

Mozilla doesn't care whether they break features, as long as they can make more money. I strongly dislike this approach by the supposedly "good" browser manufacturer.

Too many people complain about the UI and claim it's "outdated, ugly, unusable". I find that funny because you can make FF look almost like anything you want, and I personally hate chrome's UI.

No horizontal tab grouping. Tab groups on Chrome are perfect, and the Firefox tab extensions all suck in comparison.

That said, I'm still using Firefox today because the internet is unusable without a good ad blocker.

I have no idea either. Sure, chrome is a little faster but its a minor difference in my opinion. Been using it for a long time and have no idea why it's so unpopular.

Some js is a bit slower. I typically use chrome for self hosted apps, jupyter etc.

I think wasm performance is actually better in Firefox though.